volcanoes and the mantle in rifts -...

Volcanoes and the Mantle in Rifts

Tobias Fischer University of New Mexico

Albuquerque, Rio Grande Rift

Rio Grande Rift

Bastow et al., 2010

Northern East African Rift

Crossey et al., 2010 Sine et al., 2008

Hydrated lithosphere during earlier subduction (60 Ma)

Mantle Plume

Nature and Role of Mantle Fluids (melts, volatiles) Importance of integrated studies (cross-discipline and geography)

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Depiction of the Nyiragongo and Nyamuragira volcanoes, based on data from theShuttle Radar Topography Mission, Advanced Spaceborne Thermal Emissionand Reflection Radiometer, or Aster, and Landsat. Some lava flows (not all) fromthe 2002-01-17 eruption are shown in red.

Nyamuragira

Nyiragongo



Around 10:00 p.m. local time on November 27, 2006, Mount Nyamulagiraerupted.

1 Mt

Stratospheric SO2 emission during eruptions

TOMS group, NASA

1 Mt

Stratospheric SO2 emission during eruptions

TOMS group, NASA

9 - 11 Mega tons of SO2 per km3 of erupted magma (Carn & Bluth, 2003) Iceland flood basalts: 5-9 Mega tons of SO2 per km3 of erupted magma (Thordarsson & Self, 2003)

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SiO2 (wt%)

Rio Grande RiftEast African RiftMid African RiftAntarctic RiftMORBglobal nephelinites

subalkaline

alkaline

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SiO2 (wt%)

Rio Grande RiftEast African RiftMid African RiftAntarctic RiftMORBglobal nephelinitesAleutian ArcCentral America

subalkaline

alkaline

Great Variety of Rock Compositions!



Spectacularly Active Volcanoes!

The East African Rift ~ 3000 km long Western and Eastern Branch Extensive volcanism (~20% rhyolites/ignimbrites) Earliest Volc. 45 Ma (S-Ethiopia) Huge Shield Volcanoes Ethiopia Flood basalts (30 - 1 Ma) Map of the East African Rift system (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Tertiary volcanic rocks plate trajectories from 50 m.y. to 10 m.y. S-Ethiopia was positioned over Kenya plume 50 m.y. ago Two Plumes Afar and Kenya (e.g. Ebinger et al., 1989)

George et al., 2010

Continental Flood Basalt Provinces are related to mantle plumes (e.g. White and McKenzie, 1995)

Plume locations and eruption rates

Afar Plume

George et al., 2010

Plume locations and eruption rates

Afar Plume

George et al., 2010

Average Iceland, Hawaii

RGR ~ 0.0002 km3/yr

Southern NM Calderas ~ 33 - 28 Ma Additional ~ 5000 km3

0.01 km3/yr

The East African Rift

Chondrite-normalized REE variation diagram for examples of the four magmatic series of the East African Rift (after Kampunzu and Mohr, 1991), Magmatic evolution and petrogenesis in the East African Rift system. In A. B. Kampunzu and R. T. Lubala (eds.), Magmatism in Extensional Settings, the Phanerozoic African Plate. Springer-Verlag, Berlin, pp. 85-136. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

MORB

OIB

Enrichment in LILE compared to MORB -> similar to OIB or Plume

East African Rift System. a. Pre-rift stage,

asthenospheric mantle rises into the lithosphere. Decompression melting produces variably alkaline melts. Some partial melting of the metasomatized sub-continental lithospheric mantle (SCLM) may also occur.

b. Rift stage: development of continental rifting, eruption of alkaline magmas (red) mostly from a deep asthenospheric source.

c. Afar stage, in which asthenospheric ascent reaches crustal levels. This is transitional to the development of oceanic crust. After Kampunzu and Mohr (1991),

Winter (2001) An Introduction to Igneous and Metamorphic Petrology.

Anisotropy: Large-scale mantle flow in astenosphere associated with the superplume

Bastow et al., 2010

astenosphere

Plume location

Bastow et al., 2010

Bastow et al., 2010

EAGLE

Rooney et al., 2007

Geochemical/petrologic considerations

Wonjii Fault Belt

Rooney et al., 2007


Rooney et al., 2007

OIB-like REE


Plume R/Ra > 9

Helium isotopes (phenocrysts, gas) Pik et al., 2006

Deep Plume “like Iceland”

Shallow mantle upwelling < 400 km

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East AfricaCentral AmericaRGR

Georoc database and Mike Carr’s data base

Aqueous Fluids from Slab in ARCS

FLUIDS??

Melt inclusions: pre-eruptive melt volatile contents

Allow for assessment of pre-eruptive melt composition since they are assumed to be less susceptible to degassing and contamination than glasses

100µm

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H2O (wt%)

Volcanic Arcs

2 kbar

3 kbar

5 kbar

Etna

Fuego, Guatemala

Cerro Negro,Nicaragua

Open-systemdegassing

Georoc database and Roggensack et al., 2001

N-MORB


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H2O (wt%)

Volcanic Arcs

2 kbar

3 kbar

5 kbar

Etna

Fuego, Guatemala

Cerro Negro,Nicaragua

Open-systemdegassing

Georoc database and Roggensack et al., 2001

Kilauea

N-MORB

E-MORB

‘fields’ from Wallace, 2005


Schmidt+Poli, 1998

Slab dehydration

In Arcs fluids come from the slab

Trace amounts of H2O enhance melting….

Hirth & Kohlstedt, 1996; Asimow & Langmuir, 2003

From: Hirschman’s MARGINS talk WHOI 2006

Dasgupta & Hirschmann (2006) - Nature From: Hirschman’s MARGINS talk WHOI 2006

CO2 also enhances melting….

~wt% CO2

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H2O (wt%)

African Rifts

Suh, 2008 Georoc MI data-base (last update 2010)

Kilauea

E-MORB

N-MORB

Melt inclusions (Lavas-olivines) -not much data! (yet)

Degassing?

‘fields’ from Wallace, 2005

Mt. Cameroon

Gas sampling (fumaroles; springs;cold, pure CO2 vents)

Rungwe-region, Southern Tanzania

1.0E+07

1.0E+08

1.0E+09

1.0E+10

1.0E+11

1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09 1.0E+10 1.0E+11 1.0E+12 1.0E+13

N2/3He

CO2/3He

2005 gases2009 gasesArc Central America2006 gasesRungwe Region

AIR

CO2 and N2 richSediments

Mantle w/ CO2 100 -300ppm

Mantle w/ 1% CO2

CO2 (and Nitrogen) in Gas Emissions (Lengai and Rungwe)

0.01% Non-mantle CO2 N2

Fischer et al. 2009 and Barry, Hilton et al., 2009 AGU

1.0E+07

1.0E+08

1.0E+09

1.0E+10

1.0E+11

1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09 1.0E+10 1.0E+11 1.0E+12 1.0E+13

N2/3He

CO2/3He

2005 gases2009 gasesArc Central America2006 gasesRungwe Region

AIR

CO2 and N2 richSediments

Mantle w/ CO2 100 -300ppm

Mantle w/ 1% CO2

CO2 (and Nitrogen) in Gas Emissions (Lengai and Rungwe)

0.01% Non-mantle CO2 N2

Fischer et al. 2009 and Barry, Hilton et al., 2009 AGU

RGR (Crossey et al., )

Rio Grande Rift

Crossey et al., 2010

Suh, 2008; Wilding, 1993; Lowenstern, 1997 DUNBAR N. W.(1992)

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H2O (wt%)

African RiftsRio Grande Rift

Melt inclusions (Lavas) -not much data! (yet)

Kilauea N-MORB

Max solubility 4 kbar (NNO+4)

sulfide solubility 4 kbar (NNO-2)

Suh, 2008; Wilding, 1993; Lowenstern, 1997 DUNBAR N. W. (1992)

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H2O (wt%)

African RiftsRio Grande Rift

Melt inclusions (Lavas) -not much data! (yet)

Kilauea N-MORB

Max solubility 4 kbar (NNO+4)

sulfide solubility 4 kbar (NNO-2)

Cerro Negro

Fuego

OLD 1 OLD 2H2O 85.35 76.84CO2 14.13 22.80

Stotal 0.128 0.104SO2 0.060 0.039H2S 0.068 0.066HCl 0.068 0.044HF n.m. n.m.

He 0.0004 0.0001H2 0.2299 0.1633Ar 0.0014 0.0003O2 0.0009 n.d.N2 0.0687 0.0276

CH4 0.0002 0.0001CO 0.0242 0.0169

in mol % total gas

Oldoinyo Lengai Gas

Volatiles analyzed by SIMS (DTM) July 4 2005 Carbonatite Lava flow

N- MORB

MORB glasses and arc melt inclusions from Wallace, 2005

Arcs

wt% H2O CO2 (wt%) S (ppm) Cl (ppm) F (ppm)0.022376 9.69 8376 9909 44950.103099 11.75 2242 5647 6400.016047 10.34 2255 5791 664

0.1-0.5 0.01-0.03 800-1500 <100

3.1-6.1 0 - 0.21 to 6000 to 4100

OLD.

OLD Nephelinite 2009: up to 0.8 wt% in glass and MI

Oldoinyo Lengai Rocks

Fischer et al., 2006 de Moor et al., AGU 2009

> > >

de Moor et al. 2010 for Anatahan, Marianas

Seawater sulffate

Sulfur Degassing Model -> estimate S content and δ34S in source

2005 & 2009

Mantle volatiles

Lengai

Fischer et al., AGU 2009 de Moor et al., AGU 2009

Nepheline glass/MI 0.8 wt% S δ34S -0.7 ‰

Some Issues related to Volcanoes and the Mantle

• Connection between mantle volatiles (H2O, CO2, S) and melt production/composition/location in rifts

• Volatile fluxes into and out of rifts not constrained • Is ‘big mantle plume’ below Afar expressed in

volatile/fluid composition at surface (beyond Helium)? • Role of mantle CO2 (experiments vs. observations) • Role of mantle sulfur in melt generation • Nature and role of metasomatism in melt

generation

volcanoes and the mantle in rifts -...

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